In a variety of welded structures such as steel skeleton constructions of buildings, bridges, industrial equipment and construction machinery, “T” joints are adopted as welded joints in many instances. In general, a “T” joint is formed by bringing a single groove face of one of members into abutment against a surface of the other member to arrange these members in a “T” pattern and forming a bead in a groove, which has been formed at an area of contact between the surface of the above-mentioned other member and the above-mentioned one member, to join these members together. As known examples of this type, there are the welding methods disclosed in JP-A-08332567 and JP-A-06023544. The former conventional technique requires advance arrangement of a bead on the back side of a groove, which is formed at an area of contact between two members, to avoid burn-through of a groove root portion. The latter conventional technique, on the other hand, requires advance arrangement of a bead on the back of a groove, which is formed at an area of contact between two members, to prevent the weld metal from punching through or any part from remaining undeposited.
As a control method for making a center of a welding torch trace a weld line upon conducting automated welding, an arc sensor is widely employed to make use of electrical changes associated with changes in arc length and wire extension when the welding torch is caused to weave in the direction of the width of a groove. As conventional art of this sort primarily for an offset in the direction of the width of a groove, it is known, as disclosed in JP-B-53011502, to compare the magnitude of an integral of welding currents obtained at left ends of weaving with that of an integral of welding currents obtained at right ends of the weaving and then to correct the welding torch leftward or rightward on the basis of a signal representative of the comparison to trace a weld line.
To prevent the burn-through of a groove root portion at an area of contact between one of members, said one member having a single groove face, and the other member against which the single groove surface is brought into abutment, the above-mentioned conventional technique includes advance arrangement of a bead at the area of contact on a side opposite to the welded side. Depending on the shape of a welded joint structure or welded structure, however, it may be difficult, from the standpoint of actually performing welding, to arrange a bead beforehand on the back side of a groove as in the above-mentioned conventional technique.
When performing automated welding, an arc sensor is widely employed as in the above-mentioned conventional technique. Conventional arc sensing methods, however, have difficulty in tracing a weld line because they are not designed to be applicable to such a welding method that by arc welding from the side of a groove, a bead is formed on the back side.
It is also difficult to trace a weld line when a move or deformation occurs in a groove in the direction of the width of the groove or in the direction of a distance to a tip of a welding wire due to restraint conditions for a first base material and second base material or a thermal distortion or the like upon welding.
With the foregoing in view, work-related limitations are considered to be eliminated provided that a bead in the form of a fillet weld can be stably formed on the back side of a groove by arc welding from the side of the groove without arranging any bead beforehand on the back side of the groove.
The present invention has been completed in view of such background circumstances, and its objects are to provide a welding method for permitting stable and efficient formation of a bead in the form of a fillet weld on a back side of a groove by arc welding from the side of the groove without arranging a bead beforehand on the back side of the groove, a welding apparatus useful for the welding method, and a welded joint and welded structure fabricated by the welding method.